Cryogenic cooling apparatus

ABSTRACT

Cryogenic cooling apparatus including a heat exchanger affording two paths through one of which refrigerant gas from a supply under pressure is supplied to a pressure reducing nozzle, whereupon the low pressure refrigerant returns through the other path, a valve member controlled by a bellows and co-operating with the nozzle to vary its effective area for automatically controlling the flow of refrigerant. To give &#39;&#39;&#39;&#39;fail open&#39;&#39;&#39;&#39; operation the valve is subject to the vapor pressure of a material which falls below the ambient pressure in the apparatus as its temperature falls and the demand for cooling drops, and arranged so that the resulting suction will then tend to close the valve against the said bias.

[541 CRYOGENIC COOLING APPARATUS 3 721' lnventorsrbavld Nell Clnpbell, Alcester; i Frank Arnold 'hirton, Cotton, both 3,320,755 '5/1967 Jepsen ..62/5l4 3,457,730 7/ 1969 Berry ..62/5l4 Primary Examiner-Meyer Perlin Attorney-Watson, Cole, Grindle & Wamon [57] ABSTRACT Cryogenic cooling apparatus including a heat exchanger affording two paths through one of which refrigerant gas from a supply under'pressure is .sup-

plied to a pressure reducing nozzle, whereupon the low pressure refrigerant returns through the other path, a valve member controlled by a bellows and co- 1 operating with the noule to vary its effective area for automatically controlling the flow of refrigerant. To

a give fail open" operation the valve is subject to the vapor pressure of a material which falls below the ambient pressure in the apparatus as its temperature falls and the demand for cooling drops, and arranged so.

that the resulting suction will then tend to close the valve against the said bias.

4Clalnn,2DrawingFlgures I oi England 731 Assigneep'lhellymaflccompnny. Llmlted,Redditch, England 221 Filed: 31970 [2!] Appl. No.: 21,603

301 r i nA nauonml-u' nm March 25,1969 Great Britain ..l5,606/69 Aprilis, 1969 Great Britain ..l9, l8 2/69 s2 u.s.n 62/514. 511 menu 19 00. [58] FieldofSenrch ..62/514- References Cited UNITED STATES PATENT 3,517,525 1970 Campbell 2/514 an :0 39 3Q 12 13/ if; 20 i 22- CRYOGENIC COOLING APPARATUS This invention relates to cryogenic cooling apparatus including a heat exchanger affording two paths through one of which refrigerant from a supply under pressure is supplied to a pressure reducing nozzle, whereupon the low pressure refrigerant returns through the other path, a valve member co-operating with the nozzle'to vary its effective area for automatically controlling the flow of refrigerant, and biased towards an open position and a movable wall connected to the valve to actuate it.

According to the invention the movable wall is subject to the vapor pressure of a material which falls below the ambient pressure of the apparatus as its temperature falls and the demand for cooling drops and is arranged so that the resulting suction will then tend to close the valve against the said bias.

The movable wall may be afforded by a bellows and the bias may be provided at least partly by the resilience of the bellows.

Thus the present invention provides a cooler which will fail open. That is to say if leakage should occur the valve will remain open so that cooling continues so long as a supply of gas is available (even though the cooling. is uncontrolled) rather than that the valve should close and shut off the cooling.

Thus for example in the case of a cooler for producing liquid air or nitrogen at a temperature of about 80K the effective temperature of the sensor might range from say 85 to 110K. The ambient pressure in the apparatus would normally be slightly above atmospheric, so a volatile material should be chosen having a subatmospheric vapor pressure over the range referred to. A suitable material might be methane whose vapor pressure would be in the region of 3 to 12 psi. absolute in the above temperature range. Thus the valve is arranged to be closed by a suction in the vapor space and to be opened by the resilience of the bellows, so that if leakage should occur and destroy this suction the valve will fail open and cooling will continue.

The cooling apparatus may otherwise be generally as described in the applicants U.S. Pat. No. 3,517,525, filed June 24, 1968.

The invention may be put into practice in various ways but one specific embodiment will be described by way of example with reference to the accompanying drawings in which:

FIG. 1 is a sectional elevation of a cooling apparatus working on the Joule Thomson principle, and

FIG. 2 is a sectional under plan view.

In the embodiment shown the cooling apparatus, like most of those of the specifications referred to above, is of elongated form, and it will be described in the position in which it would normally be used with its axis vertical and its cold end at the bottom.

The apparatus includes a tubular heat exchanger comprising an inner tubular body around which is helically wound a finned inlet tube 1 1 forming the inlet path of the heat exchanger. An external co-axial tube 12, formed in this case by the inner wall of a Dewar flask having an outer wall 13, is located round the finned coil 11 and the space between the inner body and the external tube provides the second or exhaust path of the heat exchanger for exhaust gas flowing past the fins to cool the incoming high-pressure refrigerant withing the helically coiled tube forming the inlet path. The lower end of the Dewar flask is closed to provide within it a reservoir in which the liquid working fluid can accummulate. A load to be cooled, such as an infra-red radiation detector 15, is formed on or secured to the outer face of the inner wall 12 of the Dewar flask.

Secured to the end of the tubular body 10 is an upper body 16 the lower part of which affords a bellows chamber 17 and the upper part affords an inlet coupling 18. The upper end of the helical finned tube 11 communicates with the interior of the upper part of the upper body 16 to which gaseous refrigerant, such as nitrogen under pressure, is supplied. at a temperature below its inversion temperature.

At its lower end the inner tubular bodycarries a seating member 20 in theform of a generally-cylindrical hollow body 26 having at its upper end a crescent section lug 21 projecting from it eccentrically into the lower end of the tubular body 10 to which it is secured as by welding. The lower end of the finned tube 11 enters the seating member through one side and'the latter contains a filter 22 through which the gas passes from the inlet tube 11 to an expansion orifice 25 formed in the bottom of the seating member 20.

The effective area of the expansion orifice is arranged to be controlled by means of a needlevalve 30 which is itself controlled by a bellows 31, situated within the bellows chamber 17 referred to above, through a depending part-tubular or C-section member 32 that will be referred to as a piston rod. Welded to the lower end of the piston rod, near one edge, is the upper end of a straight rod 33 which in turn is welded at its lower end to a hooked rod 34, of which the lower end passes through and is welded to a block 35 into which the valve member 30 is adjustably screwed. The upper end of the hooked rod 34 projects laterally into a slot formed in the lug 21 of the seating member so as to form a stop to limit downward movement of the valve and the needle valve 30 itself is adjusted so that in this lowermost position it just projects into the orifice 25 so as to center itself as it is raised to'close the expansion nozzle.

The upper end of the piston rod 32 is secured to the closed upper end of the bellows 31 and the lower end of the latter is secured to the lower part of the bellows chamber 16. Accordingly if the pressure in the bellows chamber outside the bellows should fail, the bellows will expand, raising the piston rod and causing the valve 30 to enter further into the expansion nozzle so as to reduce its effective area and finally cut off flow through it.

A sensor tube 40, of which the lower end forms a sensor, extends the whole length of the heat exchanger within its inner tubular body alongside the hollow piston rod. At its upper end it passes through the bottom member of the bellows chamber 16 so that its interior communicates with the space round the bellows. The sensor tube extends down past the valve and has its lower end portion squashed flat to form an extended heat conducting tail 41. The sensor tube, and the space outside the bellows inside the bellows chamber, are filled with liquid and vapor in equilibrium of a suitable material, which may or may not be the same as the refrigerant.

3 Thus, in operation, as described in the aforementioned U.S. Patent, as the liquid refrigerant collects in the outer vessel and the level of the-pool of liquid gradually rises, progressively immersing the extended tail of the sensor, the temperature of the sensor tube progressively falls, the pressure applied to the outside of the bellows falls correspondingly, and the bellows expands, raising the hollow piston rod and causing the needle valve. to progressively close the expansion orifree so as to reduce the flow of refrigerant.

The seating member 20 also carries, secured to it as by welding, a cylindrical shield surrounding the valve so that refrigerant issuing from the expansion nozzle cannot impinge directly on the sensor tube 40.

The arrangement described is suitable for applications where a construction of particular compactness and slenderness is required. Thus where the valve is ac tuated by a bellows situated within the heat exchanger (as in the US. patent referred to above) it may be practicable to reduce the external diameter of the heat exchanger, that is to say the internal diameter of the Dewar flask, to about 7% millimeters, but for certain applications this is still excessive, and a diameter of some millimeters is required. This is achieved in accordance with the invention set forth in the present applicants copending U.S application Ser. No. 21,601 in which the bellows, instead of being inside the heat exchanger, is located co-axially with it beyond its warm end, and can be of considerably greater diameter than the heat exchanger.

Under certain circumstances it has been found that objectionable oscillations of the valve can occur due to the spring-mass combination of the bellows assembly oscillating under the excitation of the flow issuing from the expansion nozzle. In order to prevent such oscillations the piston rod carries a chamber 50 secured within it as by welding and substantially filled with a loose particulate material 51, such as small phosphor bronze balls or tungsten carbide powder. The cavity is filled as full as possible so as to obtain the maximum possible mass, but so that the filling is not packed but is free to moveof its own accord. Thus if any oscillation should tend to occur the particulate mass can vibrate within the cavity out of phase with the hollow piston rod and thus damp out vibration.

Since it may not be easy to meter a small quantity of particulate material into such a minute cavity, it may be convenient to pelletize the material, using a binder such as solid carbon dioxide or ice, which is subsequently removed by evaporation.

It will be appreciated that the damping means employs space that would otherwise not be required and so adds nothing to the bulk of the apparatus.

The sensor tube 40 may be filled with any convenient volatile liquid in equilibrium with its vapor. Preferably however, in accordance with the present invention the bellows is designed and placed so that when the pressure in the same inside and outside it contracts enough to open the valve to give a fail-open" effect. A material is then chosen to fill the bellows chamber which has a subatmospheric vapor pressure in the prevailing temperature range, which in the case of nitrogen as the refrigerant, might be about 85 to 110 K. Thus a suitable sensor material would be methane. Thus the pressure outside the bellows in the bellows chamber will be lower than the pressure in the remainder of the apparatus and hence inside the bellows, the valve being adjusted so that the resilience of the bellows tends to open it. In these circumstances if any leakage should occur and destroy the suction round the outside of the bellows the valve will fail open and cooling will continue. In other words in the event of such a failure the cooler will continue to function, although naturally the supply of refrigerant will be exhausted more rapidly than if it were functioning correctly.

As indicated above the arrangement having the bellows outside theheat exchanger has the advantage that the size of the bellows is notlimited to that'of the Dewar flask, a point of particular importance where the valve is operated by suction.

It will be appreciated that the invention is not limited to the embodiment described by way of example and may be applied to a wide variety of constructions, for example those-described in the prior specifications referred to above.

What we claim as our invention and desire to secure by letters pat. is:

1. Cryogenic cooling apparatus, comprising;

an insulating housing,

a heat exchanger mounted within said housing,

a cooling chamber formed within said housing,

pressure reducing valve means mounted within said housing for regulating the How of a refrigerant to said cooling chamber,

said heat exchanger including a first path for conveying said refrigerant to said valve means from a supply source and a second path for conveying refrigerant under reduced pressure,

pressure regulating means responsive to the vapor pressure of a substance therein which is less than the ambient pressure within said apparatus and including means communicating with said cooling chamber for sensing the temperaturethereof and further including means for biasing said valve means in an open position, and

means connecting said pressure regulating means to said valve means to vary the opening of said valve means for automatically controlling the flow of refrigerant to said cooling chamber by tending to close said valve in accordance with the suction within said pressure regulating means.

2. Apparatus as claimed in claim 1 in which said pressure regulating means comprises a chamber and a bellows mounted therein and said bias is provided at least partly by the resilience of said bellows.

3. Apparatus as claimed in claim 1 wherein said refrigerant is a liquified gas at a temperature of about 80K and said substance within said pressure regulating means comprises methane.

4. Apparatus as claimed in claim 1 in which said pressure regulating means is mounted externally to said housing at an extremity thereof opposite said cooling chamber and said means connecting said pressure regulating means and said valve means comprises a piston rod extending through said heat exchanger. 

1. Cryogenic cooling apparatus, comprising; an insulating housing, a heat exchanger mounted within said housing, a cooling chamber formed within said housing, pressure reducing valve means mounted within said housing for regulating the flow of a refrigerant to said cooling chamber, said heat exchanger including a first path for conveying said refrigerant to said valve means from a supply source and a second path for conveying refrigerant under reduced pressure, pressure regulating means responsive to the vapor pressure of a substance therein which is less than the ambient pressure within said apparatus and including means communicating with said cooling chamber for sensing the temperature thereof and further including means for biasing said valve means in an open position, and means connecting said pressure regulating means to said valve means to vary the opening of said valve means for automatically controlling the flow of refrigerant to said cooling chamber by tending to close said valve in accordance with the suction within said pressure regulating means.
 2. Apparatus as claimed in claim 1 in which said pressure regulating means comprises a chamber and a bellows mounted therein and said bias is provided at least partly by the resilience of said bellows.
 3. Apparatus as claimed in claim 1 wherein said refrigerant is a liquified gas at a temperature of about 80*K and said substance within said pressure regulating means comprises methane.
 4. Apparatus as claimed in claim 1 in which said pressure regulating means is mounted externally to said housing at an extremity thereof opposite said cooling chamber and said means connecting said pressure regulating means and said valve means comprises a piston rod extending through said heat exchanger. 